A redundant robot has at least one more degree of freedom (DOF) than required for it to perform its intended function, in order to compensate for simple constraints, i.e., using an elbow up configuration as compared to an elbow down configuration to reach a target position. Hyper-redundant robots (HRR) have many more DOFs than required, which enables them to handle more constraints, such as those present in highly convoluted volumes, and at the same time enables them to perform a variety of tasks. HRRs are very versatile, as can be seen by looking at their biological counterparts, such as snakes, elephant trunks, and worms, all of which can poke into and crawl through crevices and convoluted passages, as well as manipulate objects. Starting in 1972 with Hirose's pioneering work in HRR design, as described in S. Hirose, Biologically Inspired Robots: Snake-like Locomotors and Manipulators: Oxford University Press, 1993 and followed by the work of G. S. Chirikjian and J. W. Burdick, as described in the article “A modal approach to hyper-redundant manipulator kinematics, IEEE Transactions on Robotics and Automation”, vol. 10, pp. 343-354, 1994, there has been considerable attention paid to HRR design. The maneuverability inherent in these types of mechanical structures and their compliance, i.e., their ability to conform to environmental constraints, allow them to overcome obstacles of significant complexity compared to conventional robots; hence they have become a challenge for robotic mechanism designers. Recently, other researchers, such as Yim, as described at http://robotics.stanford.edu/users/mark/bio.html; Miller in “Snake robots for research and rescue”, published by The MIT Press, Cambridge, Mass.: 2002, and Haith et al of at NASA Ames, as described in “Serpentine Robot for Planetary and Asteroid Surface Exploration”, presented as an oral presentation at the Fourth IAA International Conference on Low-Cost Planetary Missions, Laurel, Md., 2000, have extended Hirose's pioneering work on snake locomotion, where Yim and Haith used Yim's Polybot modules to design a modular hyper-redundant robot. In U.S. Pat. No. 4,683,406 to Ikeda and Takanashi for “Joint Assembly Movable Like a Human Arm”, a new two-DOF joint for snake robots that allowed a more compact design is described. This joint used a passive universal joint to prevent adjacent bays from twisting while at the same time allowing two degrees of freedom: bending and orienting. This universal joint enveloped an angular swivel joint, which provided the two degrees of freedom. The universal joint, which was installed on the outside, rendered the joint relatively bulky. The design in U.S. Pat. No. 4,683,406 was “inverted” by placing a small universal joint in the interior of the robot, as described at http://technology.jpl.nasa.gov/gallery/tech/Gallery/gallery/gl_pages/P44487.html;
This allowed for a more compact design, but came at the cost of strength and stiffness (backlash). Other known designs use cable/tendon actuation systems for driving the robot, yet these designs are somewhat cumbersome and require quite a large external driving system, as shown in the article by R. Cieslak et al, “Elephant trunk type elastic manipulator—A tool for bulk and liquid materials transportation” published in Robotica, vol. 17, pp. 11-16, 1999. Ma et. al in the article S. Ma, H. Hirose, and H. Yoshinada, “Development of a hyper-redundant multijoint manipulator for maintenance of nuclear reactors”, International Journal of Advanced Robotics, vol. 9, pp. 28 1-300, 1995, have also presented the mechanical design of a HRR and its control algorithm for the inspection of confined spaces. An actuated universal joint design was presented in the article by A. Wolf, et al, “Design and control of a mobile hyper-redundant urban search and rescue robot,” International Journal of Advanced Robotics, vol. 19, pp. 221-248, 2005. For this design, U-joint “crosses” are connected to one link with a pitch pivot joint, and to the next with a yaw pivot joint. The pitch and yaw joints are always orthogonal, and intersect along the link axes, leading to a relatively simple kinematic system. The pitch and yaw joints are actuated by linear actuators placed within the link's envelope. The links are configured such that the axes at each end of any link are parallel; thus, one link has pitch joints at both ends actuated by its two linear actuators; the next link has two yaw joints. This arrangement facilitates packaging of the two linear actuators side-by-side within the link. In V. A. Sujan, and S. Dubowsky, “Design of a lightweight hyper-redundant deployable binary manipulator”, published in ASME Journal of Mechanical Design, vol. 126, pp 29-39, 2004, there is shown a design for a new lightweight, hyper-redundant, deployable Binary Robotic Articulated Intelligent Device (BRAID), for space robotic systems. The device is based on embedded muscle type binary actuators and flexure linkages. Such a system may be used for a wide range of tasks, and requires minimal control computation and power resources. In the article by S. Hirose, et al, “Float arm V: hyper redundant manipulator with wire-driven weight-compensation mechanism,”, published in Proceedings ICRA, pp. 368-373, 2003, the authors used wires to design a wire-driven weight-compensation mechanism. The mechanism consisted of a parallelogram linkage mechanism that had an extended portion with the wired double pulley.
One of the biggest challenges in the design of a hyper-redundant long manipulator is maintaining reasonable dimensions and low self-weight, while not compromising the rigidity of the structure and its accuracy. Usually, these design criteria are counter-intuitive, since rigidity is usually achieved by use of structures having large physical dimensions and high self-weight, the latter being a particular disadvantage in long robotic manipulator arms.
Many of the prior art robotic arm implementations have these limitations, and involve complex or massive structures to provide the rigidity required by long robotic arms. There therefore exists a need for a robotic actuator link which achieves high rigidity and accuracy while still maintaining a comparatively low weight, and thus overcomes at least some of the disadvantages of prior art robotic actuator links.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.